Bomb sight



March 20, 1945.

E. W. CHAFEE ET AL BOMB SIGHT Filed Feb. 26, 1937 6 Sheets-Sheet l mvE NToRs KARL 14/. HHFEE MZKUM THEIR ATTORNEY March 20, 1945. w CHAFEE ET AL 2,371,606

BOMB SIGHT Filed Feb. 26, 1957 6 Sheets-Sheet 3 -lll ll' FNVENTORS m M CHHFEE 2 flu/n90 (I'J/R fHElR ATTORN'EY.

March 1945- E. w. cHAFEi; ETAL 2,371,606

BOMB SIGHT Filed Feb. 26, 1937 6 Sheets-Sheet 4 m7fi 38 I figlbl 50MB RELEHSE INVENTORS ,4 fnm N CHR EE Hgwnno GVANAUKEN 2'5 EJ ATTORN Y.

March 20, 1945. E CHAFEE ETAL 2,371,606

BOMB S IGHT Filed Feb. 26, 1957 6 Sheets-Sheet 5 RANGE ANGLE fnRL WCHAFEE 5 HOh/HRD OVANAUKEN 4 BY I Margin 20, 1945.

a E. w. CHAFEE EI'AL 2,371,606

BOMB SIGHT Filed Feb. 26, 1937 e Sheets-Sheet s Mar /w C7- (1717/.

INVENTORS 52R]. W. 67mm: 45 Ham/w 6'. l/n/vAuKE v BY ?atented Mar. 26), W45

norm EsKG-HT Earl W. Chafee, New York, N. Y., and Howard C.

Van Auken, Bloomfield, N. .Z, assignors to Sperry Gyroscope Company, Hnc, Brooklyn, N. Y a corporation of New York application February 26, 1937, Serial No. 128,934

(or. ss-ce.5)

2% Claims.

This invention relates to bomb sights for air craft which are designed to direct the course of the craft so that its ground track, except for citset, would pass through the target in a straight line. and which determine the exact point at which the bombs should be released to strike the target. The mechanism also preferably computes and sets in automatically the amount of offset necessary to compensate for side drift due to side winds.

More particular our invention constitutes an improvement in existing sights, whereby the optics of this system are improved by an im' proved method of stabilization both as to rolling and pitching and in azimuth.

Heretoiore, also, bomb sights could only be used accurately when the aircraft maintained the same altitude during the sighting operati0n.-

In accordance with our improvement, however, the sight may be used when the craft is descending or ascending uniformly, which .we term broadly gliding.

A further improvement consists inthe method of arriving at and determining when the straight ground tracktoward .the target is reached, and in the pilot directing system associated therewith.

A further improvenient'consists in the method of determining the range angle from ground speed, and trail. By our invention, also, the

determination of ofiset and its introduction is improved.

Referring to the drawings, showing one form our invention may assume,

Fig. 1 is a vertical section through the improved form of stabilized sight.

Fig. 2 is a plan vi'ew'of the same, out in half.

Fig. 3A and Fig. 33 together constitute a diagrammatic layout of the computing mechanism of the sight, Fig. 3A being the left hand portion of the diagram and Fig. 3B the right hand portion thereof,

Fig. 4 is a detail of one form of bomb release contact mechanism. I

Fig. 5 is a bottom plan view of the eye piece lens; showing the-bomb dropping signal which is operated at the time the bomb is to be released, and the offset indicator.

Fig. 6 is a side view of the same, partly in section.

Fig. 7 is a plan view of the stabilized reticle, showing the scale thereon. I

Fig. 8 is a similar view of the graduated eye piece or secondary reticle with the offset scale thereon.

Fig. 10 is an elevation diagram showing the,

theory or operation of the sight.

Fig. 11 is a plan View of the vectors involved in cross wind bombing.

Fig. 12 is a plan view of a chart used to obtain the setting of the retardation factor in on: ma-

chine.

Fig. 13 is a supplemental wiring diagram.

Referring first to Figs. 1 and 2, we prefer to employ an artificial horizon, such as some form or gyroscope i, to stabilize the optics rolling and pitching. As shown, the gyro rotor c s ing i is universally mounted'within a suppo rotatable framework 2 by means of a gimb .g 3, the gimbal being pivoted on major axi and thegimbalring, in turn, supporting the gyro casing i on minor axis 5. The gyroscope is preferably mounted in neutral equilibrium, but equipped with a power-aspirated erection device, such as provided by a pendulous inductor controller E and an A. C. stator supplied with three phase current, producing a rotating field, which stator winding 6 cooperates therewith, in the following manner. The controller it carries a copper ring 5' which is so located that it can move in close proximity to the stator i. This stator has a fiat three phase winding and is'supplied with three phase alternating current. The flux created by the windings rotates around a verticalaxis. As long as the ring 8' is concentrically positioned with respect to the axis or" the windings, no reaction occurs between the ring and the flux. If, however, the ring 5' is in an eccentric position. due to a tilt of the gyro, eddy currents will be created in the ring, tending to propel the ring out of the flux field in a tangential direction. The amplitude of the eddy currents is substantially proportional to the angular misalignment between ring and stator, and the resulting torque therefore precesses the gyro in a straight line'ba'ck toward the point of concentrioity at aspeed substantially proportional to the misalignment, so that the gyro axisarrives at the true vertical at zero speed.

In the wiring diagram inFig. 13, l is the three phase winding-on stator 300. The supply lines 30! and 302 can be interrupted by switch 228' actuated by a pin 228 operated by notched disc 206', while line 303 is not interrupted. Three resistors 221 are connected in series with the supply line'sand may be shorted out by switct 226, operated by the cagipg knob 225 of the azimuth gyro i2. If these resistors are in the circuit, current in the winding 1 is reduced, thereby decreasing the erection torque. If disc 206' is rotated so that pin 22! opens switch 228, the erection is cut 011 altogether. Other erecting means, actuated by other mediums, may be used with equal success without in any way changing the general principle of the above described device, which is more fully described in the copending application of 0. E. Esval and C. A. Frisehc, Serial No. 54,1304, filed February 15, 1936, for Electromagnetic erecting means for gyroseopes.

Preferably, the entire outer framework skirt 2 is mounted for rotation within a fixed frame 3 by means of roller supports ill, on which a. circular inclined trackway ll, secured to frame 2, rests. Guide rollers it may also lie-provided at the bottom of the ll.- Saidskirt 2 is normally maintained fixed in ez'unuth from a directional gyroscope l2 315), as hereinafter described, as by means of a shaft l3 carrying a pinion M meshing with an annular gear 15 on the bottom-of frame 2, so that the entire gyroscope and its con nected opiics is so stabilized. f n the top of the gyro cam'ng l is mounted the reticle it, which therefore is stabilized about all three axes. While stabilization of the reticle has been found sufficient for some purposes, we prefer to also stabilize against rolling at least the main target following reflecting prism or mirror I] and the intermediate prism R. To this end, both of said prisms are shown as mounted on forwardly extending arms is from gimbal ring 3, said arms passing around the forward gimbal pivot I, as shown in Fig. 2. Said prisms therefore are stabilized against rolling, although not necessarily stabilized against pitching. Prism I1 is shown as pivoted on transverse axis 32 in said arms is so that it may be tilted to follow the target. By so stabilizing the reflecting prism, the "false yaw of the craft, i. e. the apparent yaw of the line of sight due to rolling of the craft, is eliminated. r

From intermediate prism 48, the line of sight passes vertically upwardly into the objective lens system 20 which focussesthe image of the ground in the plane of the reticle 16, which is' located above but laterally displaced from the lens. Pref: erably, the reticle is directly over the center of thergyroscope and the line of sight from the objective lens is displaced laterally to the center of the gyroscope and thence upwardly through reflecting prisms or mirrors 2| and 22. The objective lens and prisms are. mounted on the rotatable frame 2, butv are not shown stabilized from the gyroscope, as this is unnecessary, said parts being mounted on a bracket 21 secured to frame scale I52 (Fig. at the bottom of lens 24.

For causing the prism l1 to follow the target, we have shown a bell crank lever 25 pivoted at} 28 on the frame 2] supporting the objective lens and having at its lower end a. transversely positloned channel member 28 engaging a knob 19 projecting upwardly from the back of the metal mounting of the prism l'l. Therefore any movement of the bell crank lever in the plane ofthe paper in Fig. 1, that is, fore and aft of. the craft, will rock the. prism to follow the target; but rolling of the craft will not aflect' the prism, since the prism is stabilized from the gyroscope and the knob 29 will merely slidebsck and forth in the channel 20. The belfcrank lever 25 is rock d driven from large gear 18, shown as driven from by the engagement of its upper end 3| with a member 3| moved by the computing mechanism of the sight, the lever being shown as having a knob on the end thereof to be engaged by the member 3!.

The computing mechanism is principally for the purpose of determining the point atv which to release the bomb. The horizontal distance from the target to the projection of this point on the ground is known as the range, and the angle that the line of sight makes at this time is the range angle. It is also for the purpose of determining the true ground course of the craft and for directing the pilot so the bombs trajectory will intersect the target.

For tinning the prism about its pivotal axis 32 to maintain the same on the target, we have shown the knob engaging member 3! as moved up and down from a spring 3! and a. rod 33, which rod, in turn, is moved by the rotation of the sight angle cam 34. Said cam is shown as mounted on a shaft 35 which also moves the moving contact 35 on the bomb release mech-'- anism, said shaft being shown as having a. pinion 3'! thereon meshing with a vertical rack II carrying the contact 35 (see also Fig. 4). shaft 35 is shown as driven by means of .a worm 39, a worm wheel It and a slip clutch I! from shaft 42, which, in turn, is driven through bevel gears I! from shaft 43, which, in turn, is driven through gears 44 from one side of the difierential 45. Initial setting of the prism on the target may be accomplished by a lamb 235, to which a sight angle scale 2% may be secured. Said knob is geared directly through bevel gears in to shaft-35 to turn cam 34. Another arm of said differential is shown as driven from the prism setting knob 45 through bevel gears 11 and shaft ll, while the third side of said differential is a second gear 49 (Fig. 3B) secured to the driven member or cylinder 50 of the ground speed variion SB secured to the shaft 51 of the ground speed "without changing the rate.

dial SI. Said shaft and dial, in turn, are shown as driven from pinion. on shaft I (Fig. 3A), which, in turn, is driven through bevel gears GI and SJ from a shaft 62 which carries at its outer end the ground speed synchronizing knob 63.

Therefore it will be apparent, that by adjustground speeddial 5|. Accurate adjustment of the prism is accomplished by turning knob '46,

As stated above, however, the disc I! is not variable speed factors-are interposed to take care of the effect of altitude on thebight' problem,

andalso the effect of continuous changes in altitude. .As shown, the disc 52 is rotated from a shaft 65 which carries a roller "01 aisecond varlablespeed drive which we my term the altitude variable speed drive II (HVQD). In said drive the radially dlsplaceable balls 01 are moved from rack bar l l, which'is positioned from a, pinion Said t9 on shaft ill, which, in turn, is rotated from a shaft ll. Shaft H, in turn, is positioned by means of a cam finger 12 thereon which engages a cam it, which we term, the altitude ratio cam, where H is the actual altitude of the craft and h the altitude (say 5000 feet) taken as unity in the design. With this H, the altitude ratio for 20,000 ft. altitude would be A. Said cam is gshownas mounted on a shaft it which is driven tical velocity variable speed drive and which is for the purpose of introducing the compensating factor for changes of altitude, i. e., forgliding or climbing) of the craft during the target approach. i'he rollers l9 thereof are shown as positioned radially from a rack bar so moved from a pinion 8i on shaft 82, which is rotated from a large gear 83 turned from a knob 85, by means of which the vertical velocity of glide V is set in, the value of which is indicated on a dial $5. The rotating disc he of said variable speed drive is shown as driven from the constant speed motor 55 through shaft 8?, bevel gears 88. shaft 89, gears Qt shaft 9i, gears 92, and shaft 93, which carries said rotating disc. The motor 53 also drives the rotating disc E of the altitude variable speed drive 55' by means of a large gear on shaft 95, driving gear 95 on the shaft ill of disc 9d.

The setting knob 58 is for the purpose of setting in the initial altitude, which turns shaft ll, slipping the roller l8 over the balls 19 without changing their setting.

A finger $9 engages in a notch ifib in a disc on shaft 32 when the aircraft is flying horizontally. i. e., when it has zero vertical velocity or no glide. At this time the balls '89 are at the center of the disc 86.

The data or values which are secured from the above described settings and variable speed drives are then set into the mechanism for computing the range angle or whole range and, with additional settings, the trail and ofiset. The cam 36 is so laid out that the rate of rotation of the shaft. thereof-is directly proportional to the linear ground speed. In other words, if the aircraft is approaching the target I at a uniform rate, the shaft 35 will be revolved uniformly in spite of the fact that the prism rate will slowly increase as the target is approached.

Therefore the radial position of the balls on the ground speed variable speed drive 5| is directly proportional to ground speed, the speed of the disc 52 being varied in accordance with f the altitude ratio from the variable speed drive $6. This position is indicated on-the ground speed dial 58' and transmitted through pinion 59.

sbaftfifi and gears SI, SI, with which meshes a gear it on shaft I02 which drives. through bevel'gears ms, an elongated pinion MB which positions rotationally one cam I05 of several novel three-dimensional cams. Cam (05 combines the ground speed (Gs) with a factor proportional to the time of fall of the bomb (To) and the altitude ratio so that the lift of the pin i8 thereon represents whole range (W) in accordance with the equation Said pin is shown as hearing at its upper end against a long lever I01, oneend of which is pivoted to a vertical rod iflB carrying the so.- called fixed contact 05 of the bomb release mechanism. Said lever is also positioned, however, by a second pin llfl, the lift of which repre; sents the trail, so that the lever operates to subtract trail Y from the whole range it to give the true range. The cam I05 is positioned axially by the lift of a third cam pin ill resting on a second three-dimensional cam i it, to give it a lift proportional to time of fall (To) will be afiectedby the vertical velocity of the craft (Va) at the time of release of the bomb, since that is a factor determining the averagerate of fall. Therefore we position cam H2 in accordance with two factors, one, axially in accordance with VB and, two, angularly in accordance with the instantaneous altitude at the time of release. To this end, said cam is rotatably but non-slidably mounted on a shaft 4 53, said shaft being positioned axially by means of a pinion lid on shaft H5, which meshes with rack teeth MB on said shaft, Said cam H2 is s'-own as non-rotatably mounted on a sleeve i it which also carries cam iZQ and gear PM, here inafter described, said sleeve being prevented from longitudinal movement by fixed collars ii! on shaft H3. The pinion lid is shown as set in accordance with the vertical component velocity of glide (V0) (i. e., the rate of change of altitude) from the knob 8d, the rotation of which rotates pinion ill meshing with large gear H3, which, in turn, meshes with gear H9 on shaft H5. When the airplane is flying horizontally, knob 8:1 is set so that the dial reads zero, at which time the detent 99 is in notch 108, as stated above.

The cam H2 is positioned rotationally from a long pinion I28 meshing with a large gear in secured to sleeve 3'. Pinion I20 is shown as rotated from the shaft T! of the variable seed roller 18 through intermeshing gears H2 and 422'. the latter on the shaft I20 of pinion I20. It will be remembered that the shaft Tl is initially positioned from'knob 98 in'accordance with the altitude, and if the plane is gliding, it is continuously rotated so as to-rotate shaft H in proportion to the rate of change of altitude by means of the variable speed drive 18'. Therefore the cam llZis positioned axially in accordance with the vertical velocity of glide and rotationally according to the instantaneous altitude. the cam being laid out so that the lift of te pin represents the time offall combined with the altitude.

The altitude is continuously indicated on aneriod barometer 230. the shaft I20 turning the matching pointer 23! thereon to keep this pointer matched withthe pointer on the barometer, the initial setting being accomplished by turning knob 98, the changes in altitude during a glide being continuously introduced through the- V0 variable speed drive 18'.

Since, however, bombs vary in their characterisiics, shape, density, etc., we provide an additional correction device for the axial positioning of the cam I85 to take care of the so-calied ballistic coeflicient of the bomb. This correction takes care of the difference in time of fall for bombs with different ballistic coefficients. This may he provided from a setting knob I22 mounted on an extension of shaft Iii which is threaded at 22:! into an enlarged extension 25 from earn 505. The ballistic coefficient is set on dial E25 by bob I23;

The trail pin III) is shown as actuated from a third three-dimensionai cam i2! so that the hit thereof 5.:

where B is the retardation factor of the bomb. Cam E2? is positioned axially from the lift of a pin $28 resting on a fourth three-dimensional cam 229-. Cam i2?! is shown as mounted on the same sleeve M3 as cam I12, but it is laid out so that the lift of the pin I28 is proportion to the square of the time of fall (Te)? and the altitude ratio. Cam I2? is positioned rotationally from shaft #30, which is set from setting knob EM.

' Ofsct mechanism From an inspection of Figs. 19 and. -11 it will be seen that the offset T1" may he written as Y sin d, where Y is the trail. It will also be ob served from similar triangles that angie d, that is angle TDT'=angle TOS, or in other words,

is equal to the drift angle. Since the iift of the pin iifi is the trail Y, we combine this factor with the sine of the drift angle to obtain the onset. For this purpose, the cam pin H8 is shown as turning, by its up and down moveent, a shaft M by means of a laterally extending pin 33?; which engages a forked arm I31 on shaft I35. Said shaft not only turns the trail dial I38, but also rocks a member I38 (Fig. 33) having a flat inner surface about the center of shaft 35. On said member rests a knob 548 on an extension 144 from a pivoted but laterally slidable arm MI, so thatsaid knob $48 may be moved to either side of the vertical position over Azimuth stabilizing and aligning mechanism As stated above, the sight is maintained stabilized in azimuth from the directional gyroscope i2. Said gyroscope is shown as of the usual type able platform I5] rotated from the follow-up I62. .Said nozzles differentially control, through pipes 258, a pair of bellows or other air pressure devices I53, 153', which are oppositely coupled to a sleeve I54, which is journaied a pivoted shaft 155 continuously rotated the motor 53 by means of gears Iii. At the end of said shaft is shown a friction cone or shaft I35. Said arm is shown as positioned lat- I45 rests. 0n the bottom of said plate is shown as resting an arm I41 extending from a, shaft I48 J'ournaled in bearing I48. Another arm I49 extends downwardly from said shaft I48 beside.

the observing telescope 23, and carries at its lower end a laterally displaccable pointer I'5I roadableon a scale I52 on the bottom lens of. the' telescope or eye piece 24 (see Figs. 33, 5, 6 and 8). The observer notes the reading of the pointer on said scale and thereafter, instead of aligning the cross hairs I54 of the main reticle I5 (Figs. 6 and 7) on the target, he aligns the numeral onthe main scale I55,-indicated by the pointer on the scale I52, on the target, thereby compensating for. offset.

roller I51 which is adapted to engage, on lateral displacement of said shaft, one or the other of drive discs I 58, 1'68 by means of which a. shaft 356 is driven in one direction or the other. The

cone is normally maintained in. its central orv non-driving position by means of a spring centraiizing mechanism I'III comprising a double ended bracket I'Ii having two upstanding arms W2 and I13, through the former of which the shaft I55 and the latter of which is centralized by centralizing springs I14. Shaft; I88 is shown as rotating the frame 2 through worm H5 worm wheel I15, shaft IIl, differential I18, gear H9, shaft I 3, pinion I4 and large pinion or gear I5 on the base of rotatable member 2.

The drift angle may beshown by a dial and pointer E80 actuated from theshaft I8] through gears 182, the shaft I8! being geared to shaft 512, rotated with the shaft I3 through gears I85. Shaft :8? also carries the pinion I84, which meshes with the rack I42 of the offset mechanism, thereby introducing sin d into the offset mechanism.

For initiallysetting the sight on the target, there is shown an azimuth setting knob I85 (Fig. 33) mounted on a sleeve I85 which directly turns,

through bevel gears I81, the cylinder I88 of the azimuth variable speed drive I85 (AVSD). Said roller is shown as mounted on a shaft I88 which actuates, through pinion ISI, the middle arm of the differential I18 so that turning of the knob I85 directly rotates the sight in azimuth without aflecting the position of the balls I82 of the azimuth variable speed drive I88; For positioning said balls we have shown a second knob I58 which rotates a gear I94 through intermediate idling shaft I55.- 0n the shaft of the gear I84 is a pinion I96, which meshes with rack teeth 011' bar I81, which carries the balls I92. The driving disc I88 of said mechanism is shown as continuously driven from the motor 53 through shaft I88, gears 208, shaft 91, large gears 55, 85,'etc., the motor thus directly driving all of the discs 88, 84 and I88 of the three variable speed drives, the azimuth I88, the vertical velocity 18', and the altitude drives 88'. I

Referring to Figs. 9 and 13, representing the method of approach to the target, during the preliminary approach the azimuth gyroscope is caged by pushingin knob 225. This also closes contics so that the line of sight intersects the target and at this point he uncages the azimuth gyroscope so that the optical line of sight is stabilized in azimuth. This also opens contacts 226, removing the short circuit of resistances 221 and thus reducing the erective force to normal. It also closes contact 30 3, hereinafter described. In the presence of a side wind, represented by the arrow, the plane move along the dotted course and the reticle wire will move oif the target to the left at a rate proportional to the angle between the original line of sight AT and the ground course line A--B. The bomber will then turn the azimuth synchronizing handle I93, which displaces the balls in the azimuth variable speed drive I89 and causes the sight to turn slowly to the right. Turning the hand wheel I93 also displaces the contact finger 20l on a rheostat 202, causing the pointer on the zero reading pilot director 203, which may be of the zero reading voltmeter type, to deflect to the right, thereby signalling the pilot to make a turn into the wind at a greater rate than, preferably double, the rate that the sight is being turned. It also moves finger 228 out of the notch on cam 206' to open contacts 228, shown schematically as a single contact in Fig. 3B, but fully shown in their circuit relation in Fig. 13, to break the circuit to windings l and thus eliminate all erective force as long as the craft is turning, so that the gyroscope is then truly free. The pilot will continue to turn as long as the balls are displaced from the center of the disc and the line of sight is turning relative to the stabilized line, but as the point D is approached, the hand wheel I 93 will gradually be brought back toward zero, thus reducing the rate of turn of the sight and the rate of turn of the craft. When the plane has reached the point D, a straight ground course or track will intersect the target. At this point the reticle will stay on the target without turning the sight, and the rate of turn of the sight becomes zero. The balls in the variable speed mechanism I89 will therefore be in the center of the disc I88 and the contact finger 20I on the rheostat will be in the central position. The pilot director will therefore read zero and the pilot will fly a straight course from there on, and the normal erecting force will be restored.

Preferably, at this time we make a contact 204' by the dropping of the detent 205 into a notch on disc 206 on the shaft I93 of knob I93.- In actual practice, discs 206 and 206' are combined, and the switches 204 and 228' are also combined into a multiple blade switch, operated by finger 220. They are shown separately in Fig. 3B for the sake of simplicity. The contact 204 is in circuit with contact 304 and with a small magnetic clutch 201 which operates to lock, when excited, the center arm of differential 200 so as to cause a shaft 203, driven from shaft I3 and connected to one arm of said difierential gear 209, to turn the other arm which is connected to a bracket 2I0 and normally. centralized by springs 2| I. The clutch can a only operate if both contacts 204 and 304 are closed, which is only possible after the approach to the target has reached the straight ground track. Movement of bracket 2I0 turns contact finger2 I 2 on a second rheostat 2 I 3 in circuit with pilot director 203. The pilot director is such that it will be operated when either contact 20I or 2I2 is displaced from the central position. As shown in Fig. 3B, the two rheostats 202 and 2 I3 are connected in parallel across the terminals of the battery or other source of E. M. F., B, and the moving finger 20! and M2, respectively, of

' change of their relative position.

each rheostat is connected to the opposite terminals of the pilot director or turn-signalling device 203. Therefore, when both of said fingers are in the mid position or in the same relative position on the rheostat, no signal will be shown on the indicator because the drop through each rheostat is the same. .When, however, either rheostat is moved off this position, a turn will be signalled in one direction or the other, depending upon the direction of movement. When the straight ground track is reached, the magnet 20! is energized, which will then displace contact2I2 in case of any departure of the craft from said straight ground track, thereby signalling the pilot to turn back to the straight ground track. At that time contact 20I is centralized.

It is also obvious that an automatic steering gear might be used in place of the pilot director or turn signalling device 203, the electric impulses operating to turn the rudder directly from the automatic pilot.

In Figs. 5 and 6, a little flag M6 is moved by a magnet 2I5 from one position to the other shown in Fig. 5, as a warning that the bomb is to be released, the magnet 2I5 being in circuit with the so called warning contacts 2I6 and 2I6 on the bomb dropping mechanism shown in detail in Fig. 4. When this signal is set, the pilot either presses a button to. drop the bomb or the bomb is dropped by the contact of contact buttons 36 and I09, which are in circuit with the bomb release solenoid 220, relay 22! deenergizing magnet 2I5 at this time.

The bomb dropping mechanism shown in Fig. 4 operates as follows: the lever I01, which is positioned by the cam pins I06 and IIO,-raises or lowers, as the case may be, a bar I08 guided for vertical motion by the bearing 3"]. Bar I00 carries a block 3| I, on which there is mounted pivoted arm'3I2, carrying the insulated contact I09, held in position by spring 3I3 against an adjusting screw 3I4. Block 3 also carries a spring supported insulated contact 2H5, which is-adapted for sliding engagement with contact 2 I 5, car-. ried on slider 3I5, which in turn is operated through a rack 38 from pinion 31. Also carried on the slider is the contact 36 which, when engaging contact I09, causes the closing of the bomb dropping circuits. A fixed sliding spring 3"; serves the purpose of conducting current to the contacts 2 I6 and 36.

As the success of the bombing operation depends largely upon the time at which the bomb is dropped, it is evident that it is very important to prevent the bomb dropping contacts from burning, as that would be equivalent to a gradual This novel bomb dropping mechanism achieves this in the following way, which allows the contacts to make a circuit but prevents them from ever breaking a circuit, thereby eliminating the formation of a destructive arc. When the block 3 and the slide 3I5 approach each other while the aircraft approaches the target, contact 2I6' will eventually engage contact 2I6 and'thereby close a circuit containing the relay 2I5 operating the warning signal 2. Next, contact I09 touches contact 36, closing two parallel circuits, one containing the bomb release relay 220 and the other consame time control of relays 220 and Hi has been transferred to the contacts M6 and M6, so that both relayswill stay energized until these contacts are separated. As the relative motion of slider 3 l 5 and block 3| I may continue for a while after the bomb is dropped, arm 3|2 will be turned counter-clockwise until a roller 320, made of insulating material, comes to rest on contact 2l6, thereby lifting contact I09 from contact 36 so that no mechanical sliding motion can gradually abrade these contacts. During the return of the slider 315 and the block 3| I to their initial position, contacts 36 and I09 remain shorted until contact between points H6 and M6 is broken, which happens long after contacts I09 and 36 have been separated. This combination of contacts and relays makes ,it possible to maintain the mechanical dimensions of the main contacts so 1 that after thousands of operations nochange is measurable, which could not be accomplished if the contacts have to draw an arc every time they are separated.

The importance of varying and eliminating the erecting force on the gyro-vertical in the bomb sight, as shown in Fig. 13, may be realized when it is remembered that the exact stabilization of the optics during the target approach is essential to accurate bombing. Neither a truly neutral gyroscope nor a gyroscope at all times erected at the normal rate, such as a Sperry artificial horizon, is suitable for this purpose because a neutral gyroscope will not stay vertical for any length of time because of friction and because of the earths rotation, while an erected gyroscope is subject to deflection by the action of acceleration forces on the pendulous erecting device during turns of the craft. Such deflection is directly proportional to the comparative strength of the erecting device, i. e., to the normal erection rate, so that by making the erecting device much weaker than ordinarily employed, during the target approach, the disturbing effect of any turn at this critical time is kept a minimum. Such deflection is further practically reduced to zero by eliminating the erecting efiect during signalled turns. However, when such force is made very weak, say of such a strength as to erect the gyroscope at a rate of less than a degree a minute, too much time may be taken in bringing the gyro-vertical into 7 the vertical after releasing. Therefore we prefer to increase the erecting force materially above normal, to erect the-gyroscope at the rate of, say, 10 degrees a minute or more, just prior'to the time that the target approach is begun, that is, prior to the time that the directional gyroscope is uncaged. By this combination greatly improved results have been secured in practice.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is: r

1. A time of fall mechanism for adapting bomb sights for a gliding approach, including means for setting in the present altitude, means for setting in the rate of change of altitude due to glide, a variable speed device set from said second means and adapted to alter: the altitude setting at a rate proportional to the rate of change of altie tude,'and cam means also setfrom'said second means for correcting the calculated time of fall for the initial downward velocity of the bomb when released from the gliding aircraft.

2. In a bomb sight, computing mechanism for determining time of fall, a three dimensional cam and cam pin which are relatively positioned axially and rotationally of the cam in accordance with the component vertical velocity of glide or rate of change of altitude and the instantaneous altitude, including means for originally positioning said cam in one direction in accordance with the initial altitude, means for continuously moving said cam in said direction at a rate proportional to the change of altitude, and means for moving the cam in the other direction through a distance proportional to said vertical rate, said cam. being so laid out that the lift ofthe pin thereon is a function of the time of fall of the bomb.

3. In a time of fall computing mechanism for bomb sights,'a three dimensional cam and cam pin relatively positionable axially and rotationally of the cam, means for relatively positioning said cam and pin axially in accordance with the rate of change of altitude of the craft, means for positioning the same rotationally in accordance with the initial altitude, and means for turning the same at a rate proportional to the change of altitude, said cam being so laid out that the lift of the pin is a function of the instantaneous altitude and vertical velocity at the time of release.

4. A bomb sight computing device as claimed in claim 3, a second three dimensional cam positioned axially from the lift of said first mentioned pin, and means for positioning said cam rotationally in accordance with the ground speed of the component vertical velocity of glide or rate of change of altitude and the instantaneous altitude, including means for originally positioning said cam in one direction in accordance with the initial. altitude and means for continuously moving said cam in said direction at a rate proportional to the change of altitude, said cam being so laid out that the lift of the pin thereon is a functionof the square of the time of fall of the bomb, a second three dimensional cam positioned axially from the lift of said first mentionedpin, and means for positioning said cam rotationally in accordance with the horizontal retardation rate'of the bomb, said cam being so laid out that the lift of the pin thereon is proportional to trail.

6. In a bomb sight for aircraft, the combination with an optical system rotatable in azimuth and a pilot director, manually operated means for rotating said system to maintain the sight on the targetand for simultaneous operation of said pilot director to cause turning of the craft until the straight ground track is reached, motor driven means differentially connected to said manually drivenmeans, a directional gyroscope to control said motor driven means for normally stabilizing said optical system in azimuth, and switch means for automatically transferring the control of said pilot director from said manual to said motor means upon the straight ground track bei g reached.

7. An oflset mechanism for bomb sights having ale along and adjaatqxiliary scale in the line w s a movable pointer readable r fin f. ms for automatically moving gi Di accordance with the ofiset. 191E013 et mechanism as claimed in claim '7, i said pointer moving means includes a positiened in accordance with the trail, a

t, ositioned in accordance with the sine oi the drift angle. and means for combining the movement of said parts.

9. In a bomb sight, variable speed means for turning the line of sight to keep it on the target, including a cam and cam shaft, a pin thereon the lift of which turns said line of sight, said cam being so laid out that the rate of rotation of its shaft is directly proportional to ground speed, and a bomb releasing contact actuated by the rotation of said shaft.

10. In a glide bomb sight, means for determining the rate of change of altitude, a variable speed device for maintaining the line of sight on the target, comprising a revoluble disc, a roller driven thereby, means for radially adjusting the roller on the disc according to ground speed, means for rotating the line of sight from said roller, and a second variable speed device for rotating said disc, also comprising a revoluble disc, a roller driven thereby, and means controlled by said rate for continuously adjusting said last named roller on said last named disc in accordance with the ratio of a fixed altitude to the momentary altitude.

11. In a bomb sight, a variable speed device for maintaining the line of sight on the target, including a driving part and a part driven therefrom ata relative speed proportional to its position thereon, a second variable speed device for driving said first named driving part, including a driving part and a part driven therefrom at a relativespeed proportional to its position thereon, said driven part actuating the driving part of said first device, and a third .variable speed device for positioning said driven part, including a constantly rotated driving part. a part driven therefrom at a speed proportional to its position thereon, means actuated therefrom for position-' ing the driven part of said second mentioned device, and means for positioning the driven part of said last named device in accordance with the rate of change of altitude.

" a s'meoa 12. A bomb sight as claimed in claim 11, having direct means for initially positioning the driven part of the second mentioned device in accordance with the initial altitude.

13. In a bomb sight for aircraft, an observing eye piece, an artificial horizon such as a gyrovertical, a reticle stabilized therefrom about a normally fore and aft and an athwartship axis, and an object following pivoted reflector for refleeting an image of the target on said reticle and thence into said eye piece, said reflector being stabilized by said artificial horizon about at least said fore and aft axis.

14. In a bomb sight for aircraft,- an observing eye piece, a gyro-vertical, a gimbal mounting therefor having its major axis normally fore and aft, a retiole visible in said eye piece and mounted on said gyroscope. and an object following reflector for reflecting an image of the target on said reticle pivoted on the gimbal and thence into said eye piece, whereby said reflectoris stabilized about said fore and aft axis.

15. A bomb sight as claimed in claim 13, also having direction maintaining means such as a II directional gyroscope, and means for stabilizing in azimuth therefrom said artificialhorizon and its connected reticle and reflector.

16. In a bomb sight, at gyro-vertical for stabillzing the line of sight against rolling and pitching and having an erection device, a directional gyroscope for stabilizing the line of sight in azimuth, means for normally caging said directional gyroscope and for releasing it at the beginning of target approach, switch means engaged by said means to actuate a pilot directing device for causing the craft to fly in a curved path until the straight ground track is reached, said last named means rendering said erection device substantially inoperative until the straight ground track is reached.

17. In a bomb sight, a gyro-vertical for stabilizing the line of sight against rolling and pitching during target approach below the effectiveness prior to uncaglng.

18. In a bomb sight, a gyro-vertical for stabilizing the line of sight against rolling and. pitching and having an erection device, a directional gyroscope for stabilizing the line of sight in azimuth, means for normally caging said azimuth gyroscope and for releasing it upon approaching a target, means responsive to caging and uncaging of said azimuth gyroscope for changing the eiiectiveness of said erection device while said gyroscope is uncaged, and means responsive to tuming of the craft after said directional gyroscope is uncaged for rendering said erection device inoperative.

19. In a gyro-vertical for bomb sights and the like, a neutrally mounted gyroscope, a gravitationally-responsive device mounted thereon, an electromagnetic means acting between said device and gyroscope producing a rotating field which on relative tilt of said gyroscope produces an erecting torque thereon, and means for temporarily increasing the strength of said electromagnetic means prior to a target approach and thereafter employing a much weaker means during the target approach.

20. In a gyro-vertical, a neutrally mounted gyroscope, a gravitationally responsive device mounted thereon, an electromagnetic-means acting between said device and gyroscope producing a rotating field which on relative tilt of said gyroscope produces an erecting torque thereon, and means for temporarily varying the relative strength of said electromagnetic means at will to increase, reduce and/or eliminate the erective force.

21. In a bomb sight computing mechanism for computing the trail, a three dimensional cam and cam pin which are relatively positioned axially and rotationally oi the cam in accordance with the component vertical velocity ofglide or rate of change of altitude and the instantaneous altitude, respectively, including means for originally positioning said cam in one direction in accordance with the initial altitude,

uemg so laid out mat the int 01 me pm wereon is a function of the square of the time of fall of the bomb.

22. A bomb sight computing mechanism as claimed in claim 3, having a second three-dimensional cam giving a pin lift proportional to the whole'range angle and having a, third threedimensional cam and cam pin movable with said first cam in both directions, said third cam being so laid out that the lift of the'pin thereon is a function of the square of the time of fall of the bomb, a fourth cam positioned axially from the lift of said third pin, means for positioning the same rotationally in accordance with the hori- "zontal retardation of the bomb, said cam being so laid out that the lift of the pin is proportional to trail, and means for subtracting the lift movements of said second and fourth cam pins, whereby trail is subtracted from whole range to give true range angle.

23. Means for determining the true point of 7 release in bomb sights, including two pairs of said optical means from said output member prothree-dimensional cams, cam lift pins on each of said cams, the second cam of each pair being moved in one direction by the lift of the pin on the first cam of each pair, respectively, the liltoi portionately to a predetermined function of the displacement of said output member to produce a corresponding rotation of the line of sight about an axis substantially normal to the line of flight of said bomb sight,'means for manually adjusting the displacement of said second input member so as to maintain the line of sight on the target, whereby the displacement of said output member is proportional to the instantaneous range to said target, and the displacement of said the pin on one of said second cams being whole range and the lift of the pin on the other of said second cam being trail, and means for subtracting the movements of said pins. I

2%. In a bomb sight, apparatus for determining trail, comprising a three dimensional cam, a

said gyro vertical about twoindependent axes, a directiqnalgyro, a sighting member supported for stabilization by said, gyro vertical about one of saidaxes, and means controlled by said directional gyro for stabilizing said sighting deflector about a thirdtaxis, said sighting deflector being arranged to direct an image of the target to said 1 reticle, and thence to said eye piece thereby providing a stabilized line of sight.

26. In a bomb sight, a mechanism for computing whole range comprising means settable according to instantaneous vertical velocityol' the bomb sight, meansgsettable according to ground speed, means settable according to instantaneous altitude, mechanism adjusted by said first and I third-mentioned means for determining time of second input member is proportional to ground speed, a plurality of cooperating control members, means for displacing a first of said control members proportionately to a first predetermined function of instantaneous altitude and vertical velocity, means actuated by said first-named displacing means and said second input member for displacing a second of said control members proportionately to predetermined functions 01' altitude, vertical velocity and ground speed, means for displacing a third of said control members proportionately to a second predetermined function of instantaneous altitude andvertical velocity, means for displacing a fourth of said control members by said third-named displacing means and a third input member proportionately to predetermined functions of altitude,

. vertical velocity and the retardation factor of' ing the whole range.

the bomb, a fifth control member displaced by and proportionately to the difference between the displacement of said second control member and the displacement of said fourth control member, and a bomb release actuator operable when the displacements of said fifth control member and said output member become equal.

28 In a bomb sight for aircraft, a stationary eye piece, a gyro, a reticle stabilized by said gyro about two mutually perpendicular axes, and a sighting deflector stabilized by said gyro about only one of said axes and arranged to direct an image of the target to said reticle, said si hting deflector being mounted for rotation about an axis perpendicular to said one axis independently of said gyro to follow said target.

EARL W. CHAFEE. HOWARD C. VAN AUKEN. 

